This disclosure relates to structures of trench gate type semiconductor devices performing switching operation.
Insulated gate bipolar transistors (IGBTs) having high input impedance and low on-voltage are used in motor driving circuits. The IGBTs, however, have a trade-off relation between breakdown voltage and on-voltage.
For such features of the IGBTs, a variety of approaches have been proposed to reduce the on-voltage while keeping the breakdown voltage high. For example, a structure has been proposed in which an n-type layer having a high impurity concentration than that of a drift region and configured to accumulate holes (hereinafter referred to as “carrier accumulation layer”) is arranged between abase region and the drift region. Such a structure can prevent holes from a collector region from reaching an emitter electrode, thereby decreasing the on-voltage (for example, see Japanese Patent Application Publication No. 2002-353456 (PTL 1)).